Directed self-assembly (“DSA”) processes use block copolymers to form lithographic structures. There are a host of different integrations for DSA (e.g., chemo-epitaxy, grapho-epitaxy, hole shrink, etc.), but in all cases the technique depends on the rearrangement of the block copolymer from a random, unordered state to a structured, ordered state that is useful for subsequent lithography. The morphology of the ordered state is variable and depends on a number of factors, including the nature of the block polymers, relative molecular weight ratio between the block polymers, and the annealing conditions. Common morphologies include line-space and cylindrical, although other structures may also be used. For example, other ordered morphologies include spherical, lamellar, bicontinuous gyroid, or miktoarm star microdomains.
Annealing of the block copolymer layer has traditionally been achieved by various methods known in the art, including, but not limited to: thermal annealing (either in a vacuum or in an inert atmosphere containing nitrogen or argon), solvent vapor-assisted annealing (either at or above room temperature), or supercritical fluid-assisted annealing. As a specific example, thermal annealing of the block copolymer can be conducted at an elevated temperature that is above the glass transition temperature (Tg), but below the degradation temperature (Td) of the block copolymer. However, to generate well-registered patterns, thermal annealing, solvent vapor-assisted annealing, and supercritical fluid-assisted annealing each have their own inherent limitations.
For example, thermal annealing of some block copolymers (e.g., polystyrene-b-polymethacrylate) may be accomplished in relatively short processing times. But to achieve reductions in critical dimensions and line edge roughness, the use of block copolymers with larger Flory-Huggins interaction parameter (χ) may be required. But the higher χ block copolymers generally have slower self-assembly kinetics, and self-assembled pattern generation may take a few to tens of hours, thus detrimentally affecting throughput. Solvent vapor-assisted annealing can improve the kinetics of the self-assembly of higher χ block copolymers but involves the introduction of another component to the system with its own hardware and process constraints.
Accordingly, there is a need for new apparatus and methods for annealing block copolymers in DSA applications.